Glass micro fiber media consisting of a laminate of micro glass paper and polyester nonwoven can filter contaminants such as microbiological cysts and asbestos from drinking water. This material can be formed into a pleated structure to increase useful surface area for filtration. However, forming pleats quickly and reliably in glass micro fiber media challenges existing pleating equipment. Glass micro fiber media material tends to have memory and is highly elastic in bending and resists plastic deformation. Material that bends elastically will generally not take a set when folded and can spring back to its original shape if not controlled properly. Glass micro fiber media can also be delicate to handle and can be damaged if strained excessively. A filter requiring a small pleat height, for example, less than 0.25 inches (0.64 centimeter), creates further challenges for manufacturing due to geometrical and physical constraints.
In a pleating process, forces can act upon a web in primarily three directions. The direction of travel of the web is generally known in the art as the machine direction (MD). The direction orthogonal and coplanar to web motion is generally known as the cross-machine direction (CD). The direction orthogonal to both the MD and CD is generally known as the Z-direction.
Two commercial approaches for creating pleats in glass micro fiber media webs are commonly used. The approaches are the pusher bar and rotary score pleaters. Both pusher bar and rotary score pleaters create pleats parallel to the CD of a web.
The pusher bar, also known in the art as a blade pleater, uses a reciprocating blade to produce a CD fold as the web travels in the MD. This method of forming pleats is relatively slow and requires multiple machines or CD lanes to achieve high throughput.
A rotary score pleater applies evenly spaced CD scores. The CD scored web is driven by nips on a slow MD conveyor that bends the web about the scores forming CD folds. A rotary score pleater can produce pleats faster than the pusher bar pleater, however, the individual folds are not controlled during the pleating process. In addition, webs that bend elastically run with low reliability due to the inability to positively control Z-direction movement of the pleated web.
In addition to conventional CD pleating, MD pleating methods are described in the art. Generally these MD processes were intended for more plastic materials that take a set when folded, tolerate higher strain, and have larger pleat heights.
An example of an MD pleater is described in Rosenburg, U.S. Pat. No. 4,252,591. This method constrains the web between converging “V”-shaped guides and chains, where the chains pull the web though the guides. These chains ride inside the “V” and the web is sandwiched between the chains and the guides. This method is not well suited for small pleat heights due to the relatively large chain cross-section required to generate sufficient force to drive the web. Secondly, this method produces poor pleats in a web that bends elastically because the weight of the chains must hold the web into the guides. A web that bends elastically can lift the chains out of the guides and prevent folding. Lastly, the web scoring process disclosed employs male rings that press the web into female grooves. This method of scoring produces excessive strain on the web and can lead to catastrophic failure. Moll, German Patent DE 583,894, attempts to minimize strain in a web during the formation of longitudinal corrugations by employing soft rollers. Moll does not address control of a web that bends elastically. Practically, soft rollers cannot fully press the longitudinal corrugations of a web that bends elastically into the grooves of a forming plate unless the longitudinal corrugations are very shallow. Also the pleats are not controlled in the Z-direction between successive rollers.
MacFarland, U.S. Pat. No. 1,313,712, Rowe, U.S. Pat. No. 2,335,313, and Jackson, Great Britain Patent No. GB 376,846, disclose methods for folding pleats in a web between converging belts. These methods are not practical for small pleats because this requires the use of an impractically small belt. Also, these methods cannot control a web that bends elastically because the belts are not able to resist the Z-direction spring force of the compressed pleated web.
U.S. Pat. Nos. 654,884; 813,593; 1,402,548; 1,759,844; 2,084,362; 2,164,702; 2,196,006; 2,314,757; 2,494,431; 2,986,076; 3,038,718; 3,205,791; 3,348,458, European Patent No. WO 99/47347, and British Patent No. GB 541,015 disclose systems that pull a web though a converging set of blades or guides. None of these teach driving a web during folding with blades. The friction created by pulling a web through the process can create excessive strain and damage web fibers. U.S. Pat. Nos. 136,267; 775,495; and 5,185,052 are representative of systems that form pleats or corrugations by running a material between progressive rollers. These systems have difficulty controlling the folds of a web that bends elastically between successive sets of rolls.
The present invention provides an improved apparatus for producing pleats in the MD direction, at high speed, in a delicate web that bends elastically. This process is likewise able to produce pleats in materials that easily take a set when folded or are insensitive to strain.